Electrical protective device



Aug. 18, 1931.

P. H. 'BRACE ELECTRICAL PROTECTIVE DEVICE Filed Oct. 25, 1921 INVENTOR firfer Brace.

IIKTTORNEY Patented Aug. 18, 1931 UNITED STATES PATENT OFFICE PORTER H. BRACE, F WILKINSBU RG, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC 8c MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA ELECTRICAL PROTECTIVE DEVICE Application filed October 25, 1921.

My invention relates to electrical protec tive devices and particularly to means for reducing the power of a circuit before the opening of the circuit.

One object of my invention is to provide a device of the above indicated character that shall so reduce the current and voltage in a circuit, before interruption thereof, as to eliminate the violent and destructive effects usually attending the opening of circuits of high power values.

Another object of my invention is to provide means for so reducing relatively heavy currents and voltages as to permit the use of relatively simple and economical interrupting devices for effecting the interruption of circuits of high-power.

Another object of my invention is to provide a. protective device that shall be normally inactlve and constructed to nnpose little or no additional resistance or impedance in a circuit that shall usually oppose power values above a certain limit in proportion to the power above that limit.

A further object of my invention is to provide a protective device for electric circuits that shall have a desirable time-limit characteristic to compensate for momentaryoverloads and to interrupt sustained overloads. In practicing my invention, I provide an armature of a dynamoelectric machine that is subjected to the current of a circuit to be protected without imposing any appreciable impedance to the current traversing the cir- J cuit and that is normally maintained station ary. Upon the occurrence of an overload, the armature is released to rotate and to thereby impose a counter-electromotive force on the circuit.

If the overload is only of momentary duration, the circuit will not be interrupted but a sustained overload will rotate the armature to so reduce the current in the circuit as to permit a circuit interrupter of relatively small rupturing capacity to open the circuit without damaging or violent effects.

Figure 1 of the accompanying drawings is a diagrammatic perspective View of a device embodying my invention;

Serial No. 510,335.

Fig. 2 is a detail view of a modified form of latch device therefor; and 1 Fig. 3 is a diagrammatic View of a modified form of my invention.

In F 1 the device comprises, in general, an armature, 1, apreferably separately-excited field winding 2, an armature shaft 3, stationary brushes 4 and 5 for co-operation with the armature 1, a slip-ring 6 mounted to rotate with the shaft 3, a stationary brush 7 engaging the slip ring 6 and connected to the stationary brush 4, a centrifugal circuitinterrupting device 8, and a latch mechanism 9. t

The centrifugal device 8 comprises a radial arm 10 secured, at its inner end, to the shaft 3, an arm 11 pivoted, at one end, to the outer end of the arm 10 and angularly related to the latter, a spring 12 connecting the arms 10 and 11, a brush 13 mounted on the arm 11 and connected, by a conductor 14, to the slip ring 6, and a stationary contact ring 15 connected to one conductor 16 of a circuit to be protected and adapted to engage the brush 13.

, The latch mechanism 9 comprises an arm 17 secured to the shaft 3, a pawl 18 pivotally mounted on a pin 19 and normally biased to engagement with the arm 17 by an over-thecenter spring 20, and a magnet 21having a core member 22 secured,at one end, to the pawl 18 and a coil 23 connected, "by a conductor 24, at one end, to the brush 5 and, at the other end, to a conductor 25 of the circuit to be protected. i

The shaft 3 may be provided with a certain amount of torsional turning movement, to provide for momentary overloads previous to the release thereof by the latch 9, by

having a portion thereof constructed of resilient rods 33 disposed between the armature 1 and the arm 17.

The device is connected, in the circuit to be protected, from the conductor 16, through the stationary contact ring 15, the rotatable brush 13, the conductor 14, the rotatable slip ring 6, the stationary brushes 7 and 4, the

armature 1, the stationary brush 5, the conductor 24 and the coil 23, to the conductor 25. The armature 1 is constructed to impose little or no resistance to the circuit current and is normally held stationary by the latch mechanism 9.

hen sustained overload occurs, the electromagnet 21 of the latch mechanism 9 actuates the arm 18 to a release position, where it is held, by the spring 20, to release the armature 1 which then begins to rotate. The armature is so related to the circuit that, when rotated, it generates an electromotive force in opposition to the current of the circuit. The current to be ultimately interrupted by the centrifugal interrupter 8 or by other suitable means, may be adjusted or determined to be of any desired preferably relatively small value. The centrifugal interrupter 8 may be adjusted to open at a predetermined speed to thus interrupt the current at a predetermined value. If the overload is ofshort duration, the armature will be latched in stationary position by the latch mechanism 9 but, when the overload is sustained, will gradually increase in speed of rotation until the opposing electromotive forces of the circuit and of the armature are of any desired relative values.

Iii-Fig. 2, in which similar parts are designated by similar reference characters, the arm 17, on the shaft 3, and the latch arm 18, instead of being positively locked, as in the above described form, may be provided with co-operating sloping portions 341 and 35, re spectively. The arms 17 and 18 are held in the latched position, against the tendency of the armature 1 to rotate, by the tension in the spring 20, which tension may be adjusted to any desired overload by a usual form of nut and screw device 36. Upon the occurrence of the overload, the portion Set acts against the portion 35 to force the arm 18 to its release position against a stop member 37. This arrangement avoids the necessity of providing the trip magnet 21.

In the form of my invention shown in Fi 8, the armature 1, of a usual direct-current type and of low resistance, is connected in shunt relation to an overload circuit interrupter 26.

A multipolar field structure 27 is provided with pole members 28 and windings 29 that maybe excited from any suitable source. Pole members 30 are provided with relatively heavy damper windings 31 to limit the cross flux caused by thearmature windings and to thus minimize the inductance of the armature circuit.

hen the circuit interrupter 26 is closed, little or no current flows through the armature and the latter therefore does not rotate. Thus the counter electromotive force of the armature is low and, when the circuit interrupter 26 is opened, the current is readily diverted through the armature without causing appreciable disturbances at the interrupterv When current flows through the armature, the latter impresses a counter electromotive force on the circuit and thus brings the effective electromotive force to a relatively low value.

hen a predetermined relatively low value of effective electromotive force has been attained, the circuit may be interrupted by a low-voltage release circuit interrupter 32 without undue disturbance.

By my invention, a quiet and effective circuit interrupter for high-power circuits is provided which prevents pitting and burning of circuit-interrupter contact members.

While I have shown and described my invention in its preferred form, changes may be effected without departing from the spirit and scope thereof, as set forth in the appended claims.

I claim as my invention:

1. A direct current electrical device connected in a circuit and comprising a rotatable armature normally held stationary but adapted to supply an electromotive force in opposition to the electromotive force of the circuit when it rotates responsive to a change in the circuit conditions, means for releasing the armature to permit rotation thereof, and additional means responsive, thereafter, to-the change produced by the said rotation to effect the interruption of the circuit.

2. A direct current electrical device connected in a circuit and comprising a rotatable armature normally held stationary but adapted to supply an electromotive force in opposition to the electromotive force of the circuit when it rotates, means for releasing the armature under predetermined increased circuit conditions and means for opening the circuit responsive to the decrease in current thereof after the released armature has rotated.

3. An electrical device comprising current generating movable means normally held stationary, connectedto acircuit and automatically movable in response to certain circuit conditions to reduce the current of the circuit, and means responsive to the reduced current for interrupting the circuit.

4:. Anelectrical device connected to a circuit and comprising current generating movable means normally held stationary and movable in response to certain overload conditions to oppose the current of the circuit and means actuated by the reduced current thus produced for opening the circuit.

5. The combination with a dynamo-electric machine connected in a circuit and comprising a stationary field winding and a 1'0- tatable armature, of means for normally preventing rotation of the armature and permitting it to rotate in response to certain conditions in said circuit, and means responsive to the reduced circuit condition caused by the opposing electromotive force of the armature, when rotating, to interrupt the circuit.

6. An electrical device comprising normally inoperative mean connected in a circuit and operative in response to predetermined conditions to change the current in the circuit and means responsive to the said change in current for opening the circuit.

7. An electrical device comprising means connected in a circuit and normally unaffecting said circuit, said means being responsiveto predetermined conditions of current values to change the current in the circuit, and means responsive to the current so changed for interrupting the circuit.

8. An electrical device connected in a circuit comprising a normally energized and inoperative rotatable armature and rendered operative in response to predetermined cur rent conditions to rotate and thereby change the current in the circuit and means actuated by said change adapted to interrupt said circuit.

9. An electrical device comprising a normally energized and inoperative rotatable armature connected in a circuit and rendered operative in response to predetermined current conditions to rotate and thereby change the current in the circuit and means for opening the circuit responsive to the said current change.

10. A circuit interrupter comprising a dynamo-electric machine, means for holding said machine in astationary condition, means responsive to the current through said circuit interrupter for releasing said holding means and means responsive to a predetermined condition attained by said machine after such release to interrupt the circuit therethrough.

11. A circuit interrupter comprising a dynamo-electric machine, means for holding said machine in a stationary condition, means responsive to the current through said circuit interrupter for releasing said holding means and means responsive to a predetermined speed of said machine to interrupt the circuit therethrough.

12. Circuit-interrupter apparatus comprising a dynamo-electric machine, a circuit to be interrupted in series With the machine, a circuit interrupter actuated by increased changes in the circuit conditions shunting the machine and a circuit interrupter, actu ated by a decreased change in the circuit condition, connected in the circuit.

13. Circuitdnterrupter apparatus comprising a dynamo-electric machine, means adapted to retain. the machine stationary, means responsive to the increased current in said retaining means to permit the machine to operate, and means responsive to the relation of the current of the machine to the current of the circuit to cause the circuit to be interrupted.

14. A dynamo-electric machine actuated by the current in a circuit to be interrupted, means provided to retain the machine inoperative when normal current is flowing in the circuit, the said means actuated by increased current in the circuit to procure the operation of the machine and means thereafter responsive to the change in current in the circuit to cause it to be interrupted.

15. An electrical device comprising a normally stationary rotatable armature con nected in a circuit and rotatable in response to increased current in the circuit and adapted to oppose the current in the circuit and means responsive to the reduced current condition in said circuit to procure its interruption.

In testimony whereof, I have hereunto subscribed my name this 18th day of October,

PORTER H. BRACE. 

